docs: def looks_like_xml(text):
      """Check if a doctype exists or if we have some tags."""
      if xml_decl_re.match(text):
          return True
      key = hash(text)
      try:
          return _looks_like_xml_cache[key]
      except KeyError:
          m = doctype_lookup_re.match(text)
          if m is not None:
              return True
          rv = tag_re.search(text[:1000]) is not None
          _looks_like_xml_cache[key] = rv
          return rv